The art of surveying involves the determination of unknown positions, surfaces or volumes of objects using measurements of angles and distances. For this purpose, a surveying instrument may comprise an electronic distance measuring device (EDM) which may be integrated with angle sensors in a so-called total station. A distance measuring total station combines electronic, optical and computer techniques and may furthermore be provided with a computer or control unit with writable information for controlling the measurements to be performed and for storing data obtained during the measurements. The total station may also comprise a tracking function, i.e. the total station may comprise a target tracker (or tracker unit). For tracking purposes, the total station may also include servo drives.
An optical quadrant tracker, or simply quadrant tracker, can be used to measure angular deviation of an optical radiation, e.g., a focused optical radiation such as a laser beam, from its ideal line-of-sight path and provide deviation signals indicative of the angular deviation from the ideal line-of-sight path in order to enable corrective adjustment of the line-of-sight path. The quadrant tracker typically comprises a photodetector enabling detection of a modulated signal contained in the optical radiation.
Tracking of a target in the vicinity of a measuring instrument, for instance for searching for, locking onto and/or identifying the target, may be performed using such a quadrant tracker.
Other techniques for obtaining these functionalities, and in particular for identifying the presence of a target, may be based on digital imaging using e.g. a CMOS sensor or the like. However, there is still a need to provide new methods and instruments improving these functionalities.